This project characterizes mechanisms of mitochondrial dysfunction and cardiomyopathy (CM) from nucleoside reverse transcriptase inhibitors (NRTIs) used in highly active antiretroviral therapy (HAART) for AIDS. Survival with AIDS improved since the introduction of HAART combinations that include NRTIs like zidovudine (3'-azido-2',3'-deoxythymidine; AZT) but mechanisms of mitochondrial toxicity from HAART are incompletely understood. The "DNA pol gamma hypothesis" offers a framework to explain mitochondrial subcellular pathophysiological mechanisms in HAART CM. It underscores the importance of NRTI intracellular and intramitochondrial phosphorylation by cellular kinases (to active moieties), inhibition of DNA pol gamma by NRTI triphosphates, and mtDNA depletion in tissue targets. Contributions of mtDNA mutations and mitochondrial oxidative stress (imbalance between reactive oxygen species and antioxidants) are also addressed. Targeted transgenic mice (TG) are living systems to test the "DNA pol gamma hypothesis" (based on the function of DNA pol gamma that replicates mtDNA). Targeted cardiac TGs (driven by the alpha myosin heavy chain promoter) are living systems to explore mechanisms of CM from HAART. The TGs: (t) express HIV transactivator protein (Tat) or (2) over-express human TK2 (the mitochondrial thymidine kinase) to be used with HAART protocols. The HYPOTHESIS states: Cardiac mitochondrial NRTI monophosphorylation (by TK2) and HIV Tat contribute pathophysiologically to HAART CM. AZT inhibits mtDNA replication, depletes mtDNA, alters mitochondrial ultrastructure, and causes CM. Targeted TGs that overexpress cardiac TK2 increase mitochondrial monophosphorylation of AZT (with AZT-containing HAART regimens). This leads to increased intramitochondrial AZTTP, inhibition of DNA pol-gamma polymerase function, mtDNA depletion and mutations, and CM. Targeted TG expression of Tat to cardiac myocytes inhibits cardiac GSH synthesis, depletes GSH, and causes oxidative stress that results in CM. HAART treatment of Tat TGs worsens CM. AIM1: to define mitochondrial biogenesis biochemically in CM from HAART using mtDNA and mtRNA abundance, and to define oxidative stress by abundance of 8-OHdG (in mtDNA), GSH/GSSG ratios and aconitase inactivation. AIM 2: to define CM from HAART microscopically and ultrastructurally using morphometric methods. AIM 3: to define cardiac performance in CM from HAART echocardiographically and using Langendorff preparations.